Complexity reduction of edge-detection based spatial interpolation

Abstract

 The present invention relates to an efficient implementation of a directional spatial prediction. The directional spatial prediction includes detecting an edge by means of determining a vertical and a horizontal gradient within an adjacent block, determining for each pixel to be predicted an intersection of the detected edge with a boundary row or a column of pixels of the adjacent block, and extrapolating or interpolating each pixel in the block according to the determined intersection. The intersection may be a sub-pel position. In particular, the calculation of the intersection includes dividing by a vertical or a horizontal gradient to obtain an integer slope common for the entire block to be predicted. This reduces the number of divisions to one per block. In order to increase the precision of the division, a scaling by a scaling factor depending on a value of a horizontal or vertical gradient, respectively, may be applied.

Description

[0001] The present invention relates to a directional spatial interpolation including edge detection. In particular, the present invention relates to an efficient implementation of such an interpolation.

BACKGROUND OF THE INVENTION

[0002] Spatial interpolation has been employed in many applications. In particular, spatial interpolation forms an essential part of many image and video coding and processing applications. In hybrid image or video coding algorithms, spatial prediction is typically employed for determining a prediction for an image block based on the pixels of already encoded/decoded blocks. On the other hand, spatial interpolation may also be used as a part of post processing the decoded image or video signal, in particular for error concealment.

[0003] The majority of standardized video coding algorithms are based on hybrid video coding. Hybrid video coding methods typically combine several different lossless and lossy compression schemes in order to achieve the desired compression gain. Hybrid video coding is also the basis for ITU-T standards (H.26x standards such as H.261, H.263) as well as ISO/IEC standards (MPEG-X standards such as MPEG-1, MPEG-2, and MPEG-4). The most recent and advanced video coding standard is currently the standard denoted as H.264/MPEG-4 advanced video coding (AVC) which is a result of standardization efforts by joint video team (JVT), a joint team of ITU-T and ISO/IEC MPEG groups.

[0004] A video signal input to an encoder is a sequence of images called frames, each frame being a two-dimensional matrix of pixels. All the above-mentioned standards based on hybrid video coding include subdividing each individual video frame into smaller blocks consisting of a plurality of pixels. Typically, a macroblock (usually denoting a block of 16 x 16 pixels) is the basic image element, for which the encoding is performed. However, various particular encoding steps may be performed for smaller image elements, denoted subblocks or simply blocks and having the size of, for instance, 8 x 8, 4 x 4, 16 x 8, etc.

[0005] Figure 1 is an example of a typical H.264/MPEG-4 AVC standard compliant video encoder 100. A subtractor 105 first determines differences between a current block to be encoded of an input video image (input signal) and a corresponding prediction block, which is used for the prediction of the current block to be encoded. In H.264/MPEG-4 AVC, the prediction signal is obtained either by a temporal or by a spatial prediction. The type of prediction can be varied on a per frame basis, per slice basis or on a per macroblock basis.

[0006] Macroblocks predicted using temporal prediction are called inter-encoded and macroblocks predicted using spatial prediction are called intra-encoded. The type of prediction for a video frame can be set by the user or selected by the video encoder so as to achieve a possibly high compression gain. In accordance with the selected type of prediction, an intra/inter switch 175 provides corresponding prediction signal to the subtractor 105. The prediction signal using temporal prediction is derived from the previously encoded images, which are stored in a memory 140. The prediction signal using spatial prediction is derived from the values of boundary pixels in the neighboring blocks of the same frame, which have been previously encoded, decoded, and stored in the memory 140. The memory unit 140 thus operates as a delay unit that allows a comparison between current signal values to be encoded and the prediction signal values generated from previous signal values. The memory 140 can store a plurality of previously encoded video frames. The difference between the input signal and the prediction signal, denoted prediction error signal or residual signal, is transformed resulting in coefficients, which are quantized 110. Entropy encoder 190 is then applied to the quantized coefficients in order to further reduce the amount of data in a lossless way. This is mainly achieved by applying a code with code words of variable length wherein the length of a code word is chosen based on the probability of its occurrence.

[0007] Intra-encoded images (called also I-type images or I frames) consist solely of macroblocks that are intra-encoded, i.e. intra-encoded images can be decoded without reference to any other previously decoded image. The intra-encoded images provide error resilience for the encoded video sequence since they refresh the video sequence from errors possibly propagated from frame to frame due to temporal prediction. Moreover, I frames enable a random access within the sequence of encoded video images. Intra-fame prediction uses a predefined set of intra-prediction modes. Some of the intra-prediction modes predict the current block using the boundary pixels of the neighboring blocks already encoded. Other intra-prediction modes, as template matching for example, use a search area made of already encoded pixels belonging to the same frame. The predefined set of intra-prediction modes includes some directional spatial intra-prediction modes. The different modes of directional spatial intra-prediction refer to different directions of the applied two-dimensional prediction. This allows efficient spatial intra-prediction in the case of various edge directions. The prediction signal obtained by such an intra-prediction is then subtracted from the input signal by the subtractor 105 as described above. In addition, spatial intra-prediction mode information indicating the prediction mode is provided to the entropy encoder 190 (not shown in Figure 1), where it is entropy encoded and provided together with the encoded video signal.

[0008] In the H.264/MPEG-4 AVC intra coding scheme, the spatial prediction is performed for subblocks of sizes 4 x 4, 8 x 8 or 16 x 16 pixels in order to reduce spatial redundancy. Intra-fame prediction uses a predefined set of intra-prediction modes, which basically predict the current block using the boundary pixels of the neighboring blocks already coded. The different types of directional spatial prediction refer to different edge directions, i.e. the direction of the applied two-dimensional extrapolation as illustrated in Fig. 3. There are eight different directional prediction modes and one DC prediction mode for subblocks of size 4 x 4 and 8 x 8, and three different directional prediction modes and one DC prediction mode for the macroblocks of 16 x 16 pixels.

[0009] Figure 3 schematically illustrates the eight directional prediction modes used for the subblocks of 4 x 4 pixels. Eight of the prediction modes are labeled by a value 302 of range {0,1,3,4,5,6,7,8} and associated with predictions in eight different directions 301. The remaining one prediction mode is labeled by value 2 and called "DC mode". In the DC mode, all pixels in a block are predicted by a single value, which is the mean value of the surrounding reference pixels. In the eight directional modes, the reference pixels are repeated along the corresponding directions 301. For instance, the vertical mode labeled with "0" consists in repeating vertically the reference pixels of the row immediately above the current block. The horizontal mode labeled with "1" consists in repeating horizontally the reference pixels of the column immediately to the left of the current block. The remaining modes labeled with a value from 3 to 8 are diagonal prediction modes, according to which the reference pixels are diagonally repeated in the respective diagonal direction.

[0010] Within the video encoder 100, a decoding unit is incorporated for obtaining a decoded video signal. In compliance with the encoding steps, the decoding steps include inverse quantization and inverse transformation 120. The decoded prediction error signal differs from the original prediction error signal due to the quantization error, called also quantization noise. A reconstructed signal is then obtained by adding 125 the decoded prediction error signal to the prediction signal. In order to maintain the compatibility between the encoder side and the decoder side, the prediction signal is obtained based on the encoded and subsequently decoded video signal which is known at both sides the encoder and the decoder. Due to the quantization, quantization noise is superposed to the reconstructed video signal. Due to the block-wise coding, the superposed noise often has blocking characteristics, which result, in particular for strong quantization, in visible block boundaries in the decoded image. In order to reduce these artifacts, a deblocking filter 130 is applied to every reconstructed image block.

[0011] In order to be decoded, inter-encoded images require previously encoded and subsequently decoded (reconstructed) image(s). Temporal prediction may be performed uni-directionally, i.e., using only video frames ordered in time before the current frame to be encoded, or bidirectionally, i.e., using also video frames following the current frame. Uni-directional temporal prediction results in inter-encoded images called P frames; bi-directional temporal prediction results in inter-encoded images called B frames. In general, an inter-encoded image may comprise any of P-, B-, or even I-type macroblocks. An inter-encoded macroblock (P- or B- macroblock) is predicted by employing motion compensated prediction 160. First, a best-matching block is found for the current block within the previously encoded and decoded video frames by a motion estimator 165. The best-matching block then becomes a prediction signal and the relative displacement between the current block and its best match is signalized as motion data in the form of three-dimensional (one temporal, two spatial) motion within the bitstream comprising also the encoded video data. In order to optimize the prediction accuracy, motion vectors may be determined with a spatial sub-pixel resolution e.g. half pixel or quarter pixel resolution. This is enabled by an interpolation filter 150.

[0012] For both, the intra- and the inter-encoding modes, the differences between the current input signal and the prediction signal are transformed and quantized by the unit 110, resulting in the quantized coefficients. Generally, an orthogonal transformation such as a two-dimensional discrete cosine transformation (DCT) or an integer version thereof is employed since it reduces the correlation of the natural video images efficiently. After the transformation, low frequency components are usually more important for image quality than high frequency components so that more bits can be spent for coding the low frequency components than the high frequency components. In the entropy coder, the two-dimensional matrix of quantized coefficients is converted into a one-dimensional array. Typically, this conversion is performed by a so-called zig-zag scanning, which starts with the DC-coefficient in the upper left corner of the two-dimensional array and scans the two-dimensional array in a predetermined sequence ending with an AC coefficient in the lower right corner. As the energy is typically concentrated in the left upper part of the two-dimensional matrix of coefficients, corresponding to the lower frequencies, the zig-zag scanning results in an array where usually the last values are zero. This allows for efficient encoding using run-length codes as a part of/before the actual entropy coding. H.264/MPEG-4 AVC employs scalar quantization 110, which can be controlled by a quantization parameter (QP) and a customizable quantization matrix (QM). One of 52 quantizers is selected for each macroblock by the quantization parameter. In addition, quantization matrix is specifically designed to keep certain frequencies in the source to avoid losing image quality. Quantization matrix in H.264/MPEG-4 AVC can be adapted to the video sequence and signalized together with the video data.

[0013] The H.264/MPEG-4 AVC includes two functional layers, a Video Coding Layer (VCL) and a Network Abstraction Layer (NAL). The VCL provides the encoding functionality as briefly described above. The NAL encapsulates information elements into standardized units called NAL units according to their further application such as transmission over a channel or storing in storage. The information elements are, for instance, the encoded prediction error signal or other information necessary for the decoding of the video signal such as type of prediction, quantization parameter, motion vectors, etc. There are VCL NAL units containing the compressed video data and the related information, as well as non-VCL units encapsulating additional data such as parameter set relating to an entire video sequence, or a Supplemental Enhancement Information (SEI) providing additional information that can be used to improve the decoding performance.

[0014] In order to improve the image quality, a so-called post filter 280 may be applied at the decoder side 200. The H.264/MPEG-4 AVC standard enables sending of post filter information for such a post filter via the SEI message. The post filter information is determined at the encoder side by means of a post filter design unit 180, which compares the locally decoded signal and original input signal. In general, the post filter information is an information allowing decoder to set up an appropriate filter. It may include directly the filter coefficients or another information enabling setting up the filter. The filter information, which is output by the post filter design unit 180 is also fed to the entropy coding unit 190 in order to be encoded and inserted into the encoded signal.

[0015] Figure 2 illustrates an example decoder 200 compliant with the H.264/MPEG-4 AVC video coding standard. The encoded video signal (input signal to the decoder) bitstream first passes to entropy decoder 290, which decodes the quantized coefficients, the information elements necessary for decoding such as motion data, mode of prediction etc., and the post filter information. In the entropy decoder 290, a spatial intra-prediction mode information is extracted from the bitstream, indicating the type/mode of the spatial prediction applied to the block to be decoded. The extracted information is provided to the spatial prediction unit 270 (not shown in Figure 2). The quantized coefficients are inversely scanned in order to obtain a two-dimensional matrix, which is then fed to inverse quantization and inverse transformation 220. After inverse quantization and inverse transformation, a decoded (quantized) prediction error signal is obtained, which corresponds to the differences obtained by subtracting the prediction signal from the signal input to the encoder in the case no quantization noise is introduced.

[0016] The prediction signal is obtained from either a temporal or a spatial prediction 260 and 270, respectively, which are switched 275 in accordance with a received information element signalizing the prediction applied at the encoder. The decoded information elements further include the information necessary for the prediction such as prediction type in the case of intra-prediction (a spatial intra-prediction mode information) and motion data in the case of motion compensated prediction. Depending on the current value of the motion vector, interpolation of pixel values may be needed in order to perform the motion compensated prediction. This interpolation is performed by an interpolation filter 250. The quantized prediction error signal in the spatial domain is then added by means of an adder 225 to the prediction signal obtained either from the motion compensated prediction 260 or intra-frame prediction 270. The reconstructed image may be passed through a deblocking filter 230 and the resulting decoded signal is stored in the memory 240 to be applied for temporal or spatial prediction of the following blocks. The post filter information is fed to a post filter 280, which sets up a post filter accordingly. The post filter is then applied to the decoded signal in order to further improve the image quality.

[0017] In video coding, intra-coded blocks within both spatially and temporally predicted images serve for refreshing the video sequence and stopping the error propagation. However, the efficiency of the spatial encoding is lower then the performance of the temporal encoding, which leads to a lower overall compression gain as well as to high variations of the resulting bitrate. In order to increase the coding efficiency, EP 2 081 386 A1 provides an improved spatial prediction in which the number of extrapolation directions for predicting pixels of a block is not limited to eight. Rather, edge detection is performed within the already decoded neighboring blocks. Based on a direction of the edge determined as dominant, the pixels of the block are extrapolated or interpolated possibly from a sub-pel position within the line of pixels belonging to a neighboring block.

[0018] EP 2 081 386 A1 enables a more precise determination of the prediction direction. This leads to a more precise spatial prediction, which, on the other hand, results in smaller prediction error signal and thus, to a better compression. However, the edge detection and the extrapolation or interpolation in the direction of the detected dominant edge require a plurality of rather complex calculations such as divisions, which increases the complexity and reduces the easiness of implementation of the encoding and/or decoding. In a lot of applications it is necessary that at least the decoder has as low complexity as possible. In particular, employment in devices with a limited power supply and/or processing means requires low-complexity implementations of an encoder and/or a decoder.

SUMMARY OF THE INVENTION

[0019] The aim of the present invention is to provide an efficient implementation of spatial extrapolation or interpolation of pixels along every possible edge direction for encoding and decoding of an image block with a reduced complexity.

[0020] This is achieved by the subject matter of the independent claims.

[0021] Advantageous embodiments of the invention are subject to the dependent claims.

[0022] It is the particular approach of the present invention to first calculate an integer slope of the detected edge based on a vertical and a horizontal gradient once per block and to then calculate an intersection of an edge with this integer slope and a row or a column of boundary pixels of an adjacent block. The prediction of the pixels is based on the position of the calculated intersection. This provides the advantage of calculating the slope only once per block. Since the calculation includes a division, it is rather complex.

[0023] In accordance with an aspect of the present invention, a method is provided for spatially predicting the values at each pixel position of a block of pixels in an image. First, an edge entering the block is detected by obtaining its horizontal gradient and its vertical gradient. Then an integer value of a slope of the detected edge is determined based on the obtained horizontal gradient and/or vertical gradient. For each pixel then a sub-pel position is determined within a closest row or column of pixels of a neighboring block, wherein the sub-pel position is calculated as an intersection of said row or column of pixels with a line having the obtained integer value slope and passing through said pixel. Each pixel in the block is then predicted (extrapolated or interpolated) based on the sub-pel position interpolated for said pixel.

[0024] In accordance with another aspect of the present invention, an apparatus for spatially predicting the values at each pixel position of a block of pixels in an image is provided. The apparatus comprises: an edge detector for detecting an edge entering the block by obtaining its horizontal gradient and its vertical gradient; an intersection determining unit for obtaining an integer value of a slope of the detected edge based on the obtained horizontal gradient and/or vertical gradient, and for determining for each pixel a sub-pel position within a closest line of pixels of an adjacent block, the sub-pel position being calculated as an intersection of said line of pixels with a line having the obtained integer value slope and passing through said pixel; and an predicting unit for predicting each pixel in the block based on the sub-pel position determined for said pixel.

[0025] The obtaining of the integer slope may include, in particular, dividing the vertical gradient by the horizontal gradient or dividing the horizontal gradient by the vertical gradient. The interpolation may include for each pixel calculating said pixel as a weighed average of full-pel positions closest to the determined sub-pel position within the line of pixels. The weights are advantageously set according to the distance of the closest pixels and the determined sub-pel position.

[0026] Preferably, the obtaining the integer slope includes scaling with a c-th power of 2, wherein c is an integer number. Moreover, the determining for each pixel the sub-pel position comprises multiplying the scaled slope with a column or a row coordinate of said pixel within the block to be interpolated and rescaling the result including shifting right by c. This scaling enables increasing of the precision of the division. Selecting the scaling factor as a c-th power of two further enables an efficient implementation of scaling and rescaling by means of left and right bit shifts, respectively.

[0027] Preferably, the value c is a function of the horizontal or the vertical gradient. This enables scaling the division ratio by a smaller value if the gradient is large in order to avoid an overflow.

[0028] Advantageously, the obtaining of the integer slope includes dividing by the vertical or the horizontal gradient implemented by retrieving the result of the division from a division table stored in a memory. The memory may be an internal memory to the device performing the interpolation or an external memory. Tabularizing the division enables the complete avoiding of division calculation. Preferably, the division tabularized is a division of a predetermined number by the vertical or the horizontal gradient. The predetermined number is advantageously an a-th power of two, a being a positive integer. Still preferably, the value of a is a function of the horizontal or the vertical gradient, in particular of the gradient applied as a divisor. This enables selecting higher a for a larger divisor and lower a for a lower divisor resulting in a further increase of the precision.

[0029] Preferably, the division table has a limited number of entries for values of the vertical gradient or horizontal gradient up to b-th power of 2, b being an integer. As long as the value of the vertical or the horizontal gradient exceeds the b-th power of 2, the vertical and the horizontal gradient are scaled by shifting their value one bit right.

[0030] According to another aspect of the present invention, a method for decoding of an image subdivided into a plurality of pixels blocks is provided, the method comprising obtaining a prediction signal block as a result of extrapolating or interpolating a current block of pixels in accordance with the above described method, and computing a reconstructed image block by adding the obtained prediction signal block to a decoded prediction error block. The reconstructed block may then be output, for instance, for displaying.

[0031] According to still another aspect of the present invention, a decoder for decoding an image subdivided into a plurality of pixels blocks is provided, the decoder comprising: an intra predictor for obtaining a prediction signal block as a result of extrapolating or interpolating a current block of pixels as described above; and reconstructor for computing a reconstructed image block by adding the obtained prediction signal block to a decoded prediction error block.

[0032] According to yet another aspect of the present invention, an encoder is provided for encoding an image subdivided into a plurality of pixels blocks, the encoder comprising: an intra predictor for obtaining a prediction signal block as a result of extrapolating or interpolating a current block of pixels as described above; subtractor for subtracting the obtained prediction signal block from the original input block to be encoded resulting in a block of prediction error signal; and an encoder for encoding the block of prediction error signal.

[0033] According to yet another aspect of the present invention, a method is provided for encoding an image subdivided into a plurality of pixels blocks, the method comprising: obtaining a prediction signal block as a result of extrapolating or interpolating a current block of pixels as described above; subtracting the obtained prediction signal block from the original input block to be encoded resulting in a block of prediction error signal; and encoding the block of prediction error signal.

[0034] In accordance with still another aspect of the present invention, a computer program product is provided comprising a computer-readable medium having a computer-readable program code embodied thereon, wherein the program code is adapted to carry out the above described method.

[0035] The above and other objects and features of the present invention will become more apparent from the following description and preferred embodiments given in conjunction with the accompanying drawings, in which:

Figure 1

is a block diagram illustrating an example of a conventional H.264/MPEG-4 AVC video encoder;

Figure 2

is a block diagram illustrating an example of a conventional H.264/MPEG-4 AVC video decoder;

Figure 3

is a schematic drawing illustrating directions along which reference pixels are extrapolated in spatial prediction of H.264/MPEG-4 AVC video coding and decoding;

Figure 4A

is a schematic drawing illustrating a direction of an edge and its coordinates;

Figure 4B

is a schematic drawing illustrating an example spatial extrapolation during which the present invention is applicable;

Figure 4C

is a schematic drawing illustrating another example spatial extrapolation during which the present invention is applicable;

Figure 4D

is a schematic drawing illustrating an example spatial interpolation during which the present invention is applicable;

Figure 5

is an example flow diagram summarizing the steps of extrapolating or interpolation according to the present invention;

Figure 6

is a block diagram illustrating a system of an encoder and a decoder employing the prediction in accordance with the present invention for intra-prediction;

Figure 7

is a schematic drawing of an overall configuration of a content providing system for implementing content distribution services;

Figure 8

is a schematic drawing of an overall configuration of a digital broadcasting system;

Figure 9

is a block diagram illustrating an example of a configuration of a television;

Figure 10

is a block diagram illustrating an example of a configuration of an information reproducing/recording unit that reads and writes information from or on a recording medium that is an optical disk;

Figure 11

is a schematic drawing showing an example of a configuration of a recording medium that is an optical disk;

Figure 12A

is a schematic drawing illustrating an example of a cellular phone;

Figure 12B

is a block diagram showing an example of a configuration of the cellular phone;

Figure 13

is a schematic drawing showing a structure of multiplexed data;

Figure 14

is a schematic drawing schematically illustrating how each of the streams is multiplexed in multiplexed data;

Figure 15

is a schematic drawing illustrating how a video stream is stored in a stream of PES packets in more detail;

Figure 16

is a schematic drawing showing a structure of TS packets and source packets in the multiplexed data;

Figure 17

is a schematic drawing showing a data structure of a PMT;

Figure 18

is a schematic drawing showing an internal structure of multiplexed data information;

Figure 19

is a schematic drawing showing an internal structure of stream attribute information;

Figure 20

is a schematis drawing showing steps for identifying video data;

Figure 21

is a block diagram illustrating an example of a configuration of an integrated circuit for implementing the video coding method and the video decoding method according to each of embodiments;

Figure 22

is a schematic drawing showing a configuration for switching between driving frequencies;

Figure 23

is a schematic drawing showing steps for identifying video data and switching between driving frequencies;

Figure 24

is a schematic drawing showing an example of a look-up table in which the standards of video data are associated with the driving frequencies;

Figure 25A

is a schematic drawing showing an example of a configuration for sharing a module of a signal processing unit; and

Figure 25B

is a schematic drawing showing another example of a configuration for sharing a module of a signal processing unit.

DETAILED DESCRIPTION OF THE INVENTION

[0036] The problem underlying the present invention is based on the observation that the efficiency of the spatial (intra) prediction applied in image and video coding can be increased by improving the precision of the edge detection and subsequent prediction. On the other hand, improving the edge detection and prediction requires more computational power and applying more complex operations such as divisions. This may cause difficulties in efficiently implementing such more complex approaches. For instance, employing only integer arithmetic for image processing speeds up the encoding and decoding and enables efficient implementations on general purpose processors, digital signal processors, or in specialized or programmable hardware. However, depending on the precision of the integer, operations such as multiplications and divisions may lead to overflows and/or decreased precision, respectively.

[0037] In order to increase the prediction performance of the intra-prediction, an improved intra prediction is employed. In particular, the improved intra-prediction relies on edge detection and calculates an intersection between a block boundary (or a plurality of them) and the edge detected as dominant. The intersection may be on a sub-pel position and the interpolation is performed based on such a sub-pel position. A corresponding example intra-prediction method is disclosed, for instance, in EP 2 081 386 A1. However, the present invention may also be used to improve the efficiency of other directional spatial prediction mechanisms.

[0038] In general, edges in an image may be detected by determining a gradient vector field of the image. A gradient vector is larger on an edge and is perpendicular thereto. One of the most popular approaches to detecting the gradient field is convolution of the image with the vertical and horizontal Sobel operator, given by the following masks:

[0039] In particular, a vertical gradient vector coordinate Gx and a horizontal gradient vector coordinate Gy in a particular pixel p(x, y) are then obtained by filtering the pixel p(x, y) with the vertical Sx and the horizontal Sy Sobel mask, respectively.

[0040] Many applications employ Sobel operator for obtaining the gradient field. However, the present invention is not limited to detecting the gradient field by means of the Sobel operator. In general, any edge detection mechanism may be employed that provides the field gradient. For instance, masks with other sizes than Sobel operator may be used such as 2x2 or 4x4, or even larger masks may be used. The selection of the particular mask depends on the desired results. Employing larger masks may add on precision of the edge detection and suppress detection of small local edges, but on the other hand, it increases the computational complexity. Alternatively, masks other than Sobel mask may be used for edge detection, such as Scharr operator, or operators based on higher derivatives.

[0041] After obtaining the vertical Gx and the horizontal Gy coordinates of the gradient G, for a plurality of pixels of blocks surrounding the block to be predicted, a dominant gradient may be determined. A dominant edge vector E with its horizontal and vertical coordinates Ex and Ey, respectively, is perpendicular on the gradient vector G. Correspondingly, the sizes of the horizontal Ex and vertical Ey components of the dominant edge vector E correspond to the sizes of horizontal Gy and vertical Gx gradient, respectively (for instance, Ex=-Gy, Ey=Gx for a counter-clock rotation). Typically, the dominant edge for a current block is determined to be an edge with a maximum norm out of edges that intersect the current block. However, other methods may be used as well, for instance, taking a weighting average of the edges, or the edge direction detected for a majority of pixels, etc. It should be noted that the calculation of gradient is not necessarily performed for all pixels of the adjacent blocks. In general, it is advantageous to only perform the gradient calculations for pixels near to the boundaries of the neighbouring block adjacent to the block to be interpolated (a current block). By calculating the gradient only for a subset of pixels in the adjacent block, the complexity is reduced. In particular, the rows and/or columns directly adjacent to the current block are not well-suited for application of a Sobel mask (or other gradient detecting mask) since the mask would only partially overlap the adjacent block. Therefore, preferably, the second and/or third nearest row or column of pixels adjacent to the current clock are used to calculate the gradient. However, the present invention is not limited thereto and other pixels in the adjacent block may be used as well.

[0042] Moreover, for the prediction, only the edges entering the block to be predicted are of importance, thus edge detection near to the boundaries also reduces the risk of detecting a false edge.

[0043] Figure 4A illustrates the edge vector E and its projections Ex and Ey (corresponding to gradients Gy and Gx, respectively) into the orthogonal axes X and Y. Figure 4B shows raster of a 4x4 pixels of the block to be extrapolated. In particular, white circles and a black square represent pixels of the block to be extrapolated. The black square 440 represents a current pixel p(x,y) the value of which is to be extrapolated in an example below. Orthogonal axis X leads through a bottom row of pixels belonging to a block adjacent to the block to be predicted on its top side. The pixels of the row are illustrated as black triangles or circles. Orthogonal axis Y leads through an utmost right column of pixels belonging to a block adjacent to the block to be predicted on its left side. The pixels of the column are illustrated as black circles. An arrow 430 illustrates the edge detected as a dominant edge E entering the block to be predicted. A dashed arrow illustratively extrapolates the dominant edge up to the current pixel p(x,y). The dominant edge E enters the block to be predicted at a sub-pel position 450 between two full-pel positions 410 and 420 (illustrated as two black triangles) under an angle α. The subbel position 450 needs to be interpolated based on its distance to the two closest full pels.

[0044] In order to preserve the sharpness, position and direction of the edge as far as possible, the current pixel 440 is extrapolated along the edge direction based on the values of both full-pel pixels 410 and 420. In this particular example, the current pixel 440 is predicted as:


wherein w₁ and w₂ are weights, which are preferably determined based on the distance of the full-pel pixels 410 and 420 from the intersection point 450. It is assumed that the point (0,0) lies near to the top left corner of the block to be predicted. For instance, the weights w₁and w₂ may be calculated as:


wherein δx is distance between the X coordinate of the current pixel 440 and the intersection 450. The operator

denotes the "floor" operation, which returns for a real operand its nearest smaller integer (in this example equal to 1). The operator

denotes the "ceil" operation, which returns for a real operand its nearest greater integer (in this example equal to 2). As can be seen in Figure 4B, the slope k of the edge 430 may be calculated as:


and thus, the distance δx may be calculated as:

[0045] Thus, the calculation of δx requires a division. In general, for each pixel of the block to be predicted, the distance δx from the x coordinate of the pixel to be predicted to the intersection point to be interpolated between the edge and the row of pixels of the top neighboring block is computed. Based on the calculated distance δx then the current pixel p(x,y) is predicted as p(x,y)=p(x-δx,0), which means that the current pixel 440 is extrapolated as value of the interpolated sub-pel position 450.

[0046] In practical implementation, all the above parameters are typically integer values with a given precision and the operations applied are integer operations. For instance, parameters Ex and Ey may be represented by corresponding 8 bits long variables. In such a case, the distance δx is also calculated using integer arithmetic by performing an integer multiplication y·Ex and then by dividing the result by Ey. In integer arithmetic division, the result is also an integer, thus, the integer division may slightly reduce the precision. In general, the reduction of precision gets higher for smaller values to be divided (y·Ex) and for greater values of divisor (Ey).

[0047] In order to reduce the number of operations performed for predicting a block of pixels as described above, according to the present invention, the number of divisions to be performed is reduced by calculating first the slope k of the edge E which is common for all pixels of the block to be predicted. The calculated slope k is to be stored as an integer slope K=int(Ex/Ey) with a predefined precision. The computed integer slope K is then used to calculate the distance δx for a particular pixel as follows:


where the notation "int" emphasizes the fact that the operand is an integer with a predefined precision. Accordingly, the division employed for computing the slope is only performed once for the entire block of pixels to be predicted. Moreover, since the y coordinate of a pixel to be predicted remains the same in same row of pixels, the distance δx only needs to be calculated once per row of pixel in the block to be interpolated. The precision of the integer is typically selected according to the implementation environment. It may be, for instance 8-bits, which is usual especially in image processing since the input pixel components are also typically sampled with 8 bits. However, the precision may be also higher such as 12, 16, or any other number of bits, or even lower than 8 bits.

[0048] However, performing the integer division ExlEy only once per block and then obtaining row-wise the distance δx may lead to reduction of the precision with respect to the solution in which the integer multiplication y·Ex is performed first and then the result is divided by Ey. This is caused by the fact that the number Ex to be divided is smaller. Moreover, the subsequent multiplication of the integer slope by the coordinate y results in further multiplicative increase of imprecision differently for different rows. In particular, the precision will be lower for higher values of y.

[0049] In order to further enhance the precision of the computation while still keeping the advantage of a single division per block, the integer slope is obtained by multiplying the number to be divided with a scaling factor 2^c, wherein c is an integer:

[0050] Advantageously, c is a positive integer. The value of c may be, for instance, any value such as a value between 1 and 4. However, other values are also possible. The particular value may be selected taking into account the block size. For instance, a possible value for c could be 4 , since the largest block size is 16x16, resulting in the highest value of y being 16 (2⁴=16). Similarly, the value of c for blocks of size 4x4 could be 2 and for blocks of size 8x8 3. This multiplication is equivalent to a left shift by c bits of the number Ex to be divided. This enlarges the value to be divided and, thus, the division by the divisor Ey will gain on precision. The distance δx can then be obtained as follows:


and the respective weights w₁ and w₂ can be calculated as follows:




or with equivalent formulas as:




wherein the operation ">>" denotes right shift by c bits, which corresponds to rescaling back by dividing the result by the applied scaling factor 2^c, the operation "<<" denotes left shift by c bits, which corresponds to multiplying by the scaling factor 2^c, and the operation "&" denotes the bit-wise logical operator "AND".

[0051] The values of δx and the weights w₁ and w₂ are non-shifted and are scaled by the factor 2^c. The right shift to divide the final result by the applied scaling factor 2^c must be done after interpolation of the subpel position:


Wherein the offset 2^c-1serves for rounding the final value to the nearest integer.

[0052] In the case the precision of the value Ex has been increased beforehand by multiplying it by 2^p, p being an integer (6 is a good value), the increase of precision through the factor 2^c has for only purpose to divide by 2^c the error introduced through the multiplication by y. For example, if the value of the integer slope is obtained by:


then, the distance δx can be obtained as follows. The error introduced through the division operation is multiplied by y/2^c and the distance δx is scaled by the factor 2^p. The scaling is necessary to calculate the distance in integer arithmetic while keeping the possibility to have a sub-pel position for the intersection point:

[0053] The weights w₁ and w₂ are obtained as follows:




and the value of the prediction is obtained by:

[0054] This calculation of the distance δx, from the x coordinate of the current pixel 440 to be predicted to the intersection of the edge with the row of pixels adjacent to the block to be predicted on the top, enables increasing the precision of the division. However, due to multiplication by y, the multiplications may result in rather high values, which, on the other hand, may cause an overflow, depending on the integer precision supported by the computing environment.

[0055] In order to maintain the increased precision of the division while avoiding the overflow, the scaling factor 2^c is selected according to the value of the vertical gradient Gy, corresponding to the value of Ex.


wherein function f(.) is an arbitrary function. Advantageously, the value of the scaling parameter c is lower for higher values of Ex.

[0056] One example for the function f(.) could be:

[0057] In such a case, c is equal to 8 for Ex equal to 1, c is equal to 1 for Ex equal to 128, and c is equal to 0 for Ex equal to 256.

[0058] If more bits are available in the system, one could define the following function:

[0059] With b the maximum number of bits available on the system.

[0060] Generally, the maximum possible precision should be used for Ex small (equal to 1 for example), and the maximum precision minus 8 bits should be used when Ex is big (close to 256).

[0061] When calculating the parameter c, the sign of the edge vector coordinate Ex is not important and thus c may, in general, also be calculated as c=f(/Ex/).

[0062] In accordance with another embodiment of the present invention, the division for calculating the integer slope of the edge is completely avoided. This is facilitated by tabularizing the division. Accordingly, a table is stored in a memory. The memory may be either an internal memory of the interpolation computing system or an external memory. The table comprises for a limited number of divisors a result of dividing a predefined value. For instance, the table may include entries with a result of a division of a number 2^a by a various values of Ey as follows:


wherein a is a positive integer. For example, a can be equal to the value of the precision p described previously. In order to keep the tabularized division as precise as possible, preferably the table division scaling factor 2^a is a function of the divisor size /Ey/:

[0063] The function g(.) is an arbitrary function. Advantageously, the value of the scaling parameter a is higher for higher size (absolute value) of Ey.

[0064] One example for the function g() could be the following:


where b is chosen so that the value b+8 does not overflow the number of bits available on the system.

[0065] Generally the maximum possible precision should be used for Ey big (close to 256) and a lower precision should be used for Ey small (close to 1). The above examples of functions f() and g() are only for illustration. The values of these functions may be either calculated on-the-fly or pre-stored in a table in memory.

[0066] The functions f() and g() may also be given by a table without referring to an analytic rule.

[0067] Then the scaled integer slope may be obtained as:


wherein the operation "sign" returns a sign of the operand and Table[.] denotes result of division by /Ey/ retrieved from a look-up table in memory. The distance δx can then be obtained similarly as in the previous embodiment by:

[0068] In that case, the distance δx is scaled by a factor 2^a. The values of the weights and the prediction of the pixels can be deduced from the previous equations by replacing p by a.

[0069] Another possibility is to keep the distance δx scaled by a factor 2^c+a. In that case, the final prediction must be right shifted in order to divide the value by 2^c+a:

[0070] In order to limit the memory requirements for storing the division table, preferably only 2^b table entries are stored. This means that /Ey/ entries only exist for 0 < |Ey| ≤ 2^b. Preferably, an entry is present in the table for each value of Ey. However, this is not necessary for the present invention and, in general, the table may list an entry only for every second, or third, etc. value of Ey. If an entry is not present, the closest entry listed in the table is retrieved. However, listing only some entries could result in a loss of accuracy.

[0071] If the divisor Ey is larger than the largest divisor listed in the table, then, preferably the value of both edge vector coordinates Ey and Ex is shifted right by one bit, corresponding to division by 2:

[0072] After the shifting, the result of division is retrieved from the table based on the new value of the divisor Ey. If the result of division was successfully retrieved, the slope δx_block is calculated as shown above. If the value of Ey is still too high, the shifting is repeated until a result of division may be obtained. With this reduction of the number of table entries, the resolution of the edge direction is slightly decreased. However, advantageously, the memory requirements are limited. By setting the parameter b, a tradeoff between the edge direction resolution and memory requirements may be set appropriately for the given computing environment as well as for the size of the block to be interpolated.

[0073] The above example has been described for an edge 430 entering from the top side the block to be predicted. Figure 4C illustrates another example in which an edge 483 enters the block to be predicted from the left side. In this example, the calculation of slope is also based on the determined gradients, however, the x and y coordinates (and correspondingly, the Ex and Ey coordinates) are exchanged. For instance, the slope is calculated as:

[0074] Consequently, the remaining computations of the distance δy₁ will be similar to those of δx in the previous example, however, the divisor now is Ex rather than Ey and instead of the vertical coordinate y of the current pixel, the horizontal coordinate x of the current pixel p(x,y) is used. Moreover, the distance δ_y1 shall be the same for a column rather than for a row of pixels in the block to be predicted. The present invention and its embodiments may be applied to this example in a corresponding way.

[0075] Another example of a possible edge direction is shown in Figure 4D. The edge intersects the left boundary of the block to be predicted. However, unlike the example described with reference to Figure 4C, the edge 482 cutting the left block boundary continues through the block and cuts 481 a bottom boundary of the top right neighboring block. In that case, the prediction is an interpolation of the edge from two directions. If the present invention is applied for intra-prediction in a system with raster scan of blocks for encoding/decoding, the top right neighbor of the block to be interpolated is already encoded/decoded and thus, its pixels may also be utilized for the prediction. In the previous examples, the prediction was performed by weighting two pixels in the full-pel positions surrounding the intersection. However, the prediction may also be performed by weighting four pixels: two pixels surrounding the intersection of the left block boundary and two pixels surrounding the intersection of the top right boundary. The weighting factors may further consider the distance of the particular intersection from the pixel to be predicted.

[0076] For simplicity, all the above examples have been described for a block of 4x4 pixels. However, the present invention is not limited to such blocks. In general, any other square and rectangular sizes of blocks such as 8x8, 16x16, 8x16, 4x8, etc. may be interpolated as described above.

[0077] Moreover, the above examples have been described mainly for deployment in image or video encoders and decoders. However, the present invention is not limited thereto. The present invention may readily be applied for other image processing tasks in which spatial extrapolation or interpolation is required. For instance, the extrapolation/interpolation according to the present invention may be used for post-processing such as error concealment.

[0078] Figure 5 summarizes the directional spatial prediction of a block of pixels according to the present invention employed in video encoding/decoding for intra prediction. An edge detecting step provides a result of edge detection: a dominant edge along which the extrapolation or interpolation is to be performed. If there is no edge detected ("no" in step 520), meaning that the neighborhood of the block to be predicted is substantially smooth, a so-called DC interpolation 530 is applied which sets all pixels of the block to be predicted to the same value given by the average value of the adjacent pixels. If, on the other hand, an edge is detected ("yes" in step 520), the slope of the edge is determined 540 and for each 550 pixel of the block the intersection of the edge with the block boundaries is determined 560, the intersecting subpel position(s) are interpolated if necessary 570 and the pixel is extrapolated or interpolated 580 accordingly.

[0079] Looking at the Figure 1 and 2, the predictor (predicting apparatus) of the present invention may be employed within the intra-frame prediction unit 170 at the encoder 100 and within the intra-frame prediction unit 270 at the decoder 200. In particular, the intra-prediction unit 170 or 270 may further comprise an edge detector, an intersection determining unit, an interpolating unit of the subpel positions in neighboring blocks and an extrapolating/interpolating unit. The edge detector detects a dominant edge cutting the block to be predicted. The intersection determining unit determines the sub-pel position corresponding to intersection of the edge determined by the edge detector and the row or column of pixels belonging to neighboring blocks surrounding the block to be predicted. The interpolating unit interpolates the value of the sub-pel position calculated by the intersection determining unit based on the values of the closest fullpel. The extrapolating/interpolating unit extrapolates/interpolates the value of the current pixel based on the subpel position(s) calculated by the intersection determining unit.

[0080] In the above examples it has been assumed that an image is encoded and/or decoded in a raster scan of blocks. This assumption causes that the adjacent blocks available for prediction are always the blocks on the top of the block to be predicted and a block left from the block to be predicted. However, the present invention will also work for different scans as long as there is at least one block already encoded/decoded adjacent to the block to be predicted and as long as there is an edge cutting the block to be predicted and passing the adjacent block.

[0081] The above examples were described for a single block of pixels. Indeed, an image subdivided into a plurality of blocks may be encoded using different encoding methods for each of the blocks. Error concealment may also be applied to single blocks. However, the present invention may also be applied to encode an entire image or frame of a video sequence.

[0082] Figure 6 illustrates an example system for transferring encoded video data from an encoder side to a decoder side in accordance with the present invention. An input video signal is encoded by an encoder 1401 and provided to a channel 1402. The encoder 1401 is an encoder implementing the directional spatial prediction in accordance with any of the embodiments of the present invention for intra prediction of at least one block as described above. The channel 1402 is either storage or any transmission channel. The storage may be, for instance, any volatile or non-volatile memory, any magnetic or optical medium, a mass-storage, etc. The transmission channel may be formed by physical resources of any transmission system, wireless or wired, fixed or mobile, such as xDSL, ISDN, WLAN, GPRS, UMTS, Internet, or any standardized or proprietary system. Apart from the encoder, the encoder side may also include preprocessing of the input video signal such as format conversion and/or transmitter for transmitting the encoded video signal over the channel 1402 or an application for transferring the encoded video signal into the storage. The encoded video signal is then obtained from the channel 1402 by a decoder 1403. The decoder 1403 is a decoder implementing the directional spatial prediction in accordance with any embodiment of the present invention as described above. The decoder decodes the encoded video signal. Apart from the decoder, the decoder side may further include a receiver for receiving the encoded video signal from a transmission channel, or an application for extracting the encoded video data from the storage, and/or post-processing means for post processing of the decoded video signal, such as format conversion.

[0083] The processing described in each of embodiments can be simply implemented in an independent computer system, by recording, in a recording medium, a program for implementing the configurations of the video coding method and the video decoding method described in each of embodiments. The recording media may be any recording media as long as the program can be recorded, such as a magnetic disk, an optical disk, a magnetic optical disk, an IC card, and a semiconductor memory.

[0084] Hereinafter, the applications to the video coding method and the video decoding method described in each of embodiments and systems using thereof will be described.

[0085] Figure 7 illustrates an overall configuration of a content providing system ex100 for implementing content distribution services. The area for providing communication services is divided into cells of desired size, and base stations ex106, ex107, ex108, ex109, and ex110 which are fixed wireless stations are placed in each of the cells.

[0086] The content providing system ex100 is connected to devices, such as a computer ex111, a personal digital assistant (PDA) ex112, a camera ex113, a cellular phone ex114 and a game machine ex115, via the Internet ex101, an Internet service provider ex102, a telephone network ex104, as well as the base stations ex106 to ex110, respectively.

[0087] However, the configuration of the content providing system ex100 is not limited to the configuration shown in Figure 7, and a combination in which any of the elements are connected is acceptable. In addition, each device may be directly connected to the telephone network ex104, rather than via the base stations ex106 to ex110 which are the fixed wireless stations. Furthermore, the devices may be interconnected to each other via a short distance wireless communication and others.

[0088] The camera ex113, such as a digital video camera, is capable of capturing video. A camera ex116, such as a digital video camera, is capable of capturing both still images and video. Furthermore, the cellular phone ex114 may be the one that meets any of the standards such as Global System for Mobile Communications (GSM), Code Division Multiple Access (CDMA), Wideband-Code Division Multiple Access (W-CDMA), Long Term Evolution (LTE), and High Speed Packet Access (HSPA). Alternatively, the cellular phone ex114 may be a Personal Handyphone System (PHS).

[0089] In the content providing system ex100, a streaming server ex103 is connected to the camera ex113 and others via the telephone network ex104 and the base station ex109, which enables distribution of images of a live show and others. In such a distribution, a content (for example, video of a music live show) captured by the user using the camera ex113 is coded as described above in each of embodiments, and the coded content is transmitted to the streaming server ex103. On the other hand, the streaming server ex103 carries out stream distribution of the transmitted content data to the clients upon their requests. The clients include the computer ex111, the PDA ex112, the camera ex113, the cellular phone ex114, and the game machine ex115 that are capable of decoding the above-mentioned coded data. Each of the devices that have received the distributed data decodes and reproduces the coded data.

[0090] The captured data may be coded by the camera ex113 or the streaming server ex103 that transmits the data, or the coding processes may be shared between the camera ex113 and the streaming server ex103. Similarly, the distributed data may be decoded by the clients or the streaming server ex103, or the decoding processes may be shared between the clients and the streaming server ex103. Furthermore, the data of the still images and video captured by not only the camera ex113 but also the camera ex116 may be transmitted to the streaming server ex103 through the computer ex111. The coding processes may be performed by the camera ex116, the computer ex111, or the streaming server ex103, or shared among them.

[0091] Furthermore, the coding and decoding processes may be performed by an LSI ex500 generally included in each of the computer ex111 and the devices. The LSI ex500 may be configured of a single chip or a plurality of chips. Software for coding and decoding video may be integrated into some type of a recording medium (such as a CD-ROM, a flexible disk, and a hard disk) that is readable by the computer ex111 and others, and the coding and decoding processes may be performed using the software. Furthermore, when the cellular phone ex114 is equipped with a camera, the image data obtained by the camera may be transmitted. The video data is data coded by the LSI ex500 included in the cellular phone ex114.

[0092] Furthermore, the streaming server ex103 may be composed of servers and computers, and may decentralize data and process the decentralized data, record, or distribute data.

[0093] As described above, the clients may receive and reproduce the coded data in the content providing system ex100. In other words, the clients can receive and decode information transmitted by the user, and reproduce the decoded data in real time in the content providing system ex100, so that the user who does not have any particular right and equipment can implement personal broadcasting.

[0094] Aside from the example of the content providing system ex100, at least one of the video coding apparatus and the video decoding apparatus described in each of embodiments may be implemented in a digital broadcasting system ex200 illustrated in Figure 8. More specifically, a broadcast station ex201 communicates or transmits, via radio waves to a broadcast satellite ex202, multiplexed data obtained by multiplexing audio data and others onto video data. The video data is data coded by the video coding method described in each of embodiments. Upon receipt of the multiplexed data, the broadcast satellite ex202 transmits radio waves for broadcasting. Then, a home-use antenna ex204 with a satellite broadcast reception function receives the radio waves.

[0095] Next, a device such as a television (receiver) ex300 and a set top box (STB) ex217 decodes the received multiplexed data, and reproduces the decoded data.

[0096] Furthermore, a reader/recorder ex218 (i) reads and decodes the multiplexed data recorded on a recording media ex215, such as a DVD and a BD, or (i) codes video signals in the recording medium ex215, and in some cases, writes data obtained by multiplexing an audio signal on the coded data. The reader/recorder ex218 can include the video decoding apparatus or the video coding apparatus as shown in each of embodiments. In this case, the reproduced video signals are displayed on the monitor ex219, and can be reproduced by another device or system using the recording medium ex215 on which the multiplexed data is recorded. It is also possible to implement the video decoding apparatus in the set top box ex217 connected to the cable ex203 for a cable television or to the antenna ex204 for satellite and/or terrestrial broadcasting, so as to display the video signals on the monitor ex219 of the television ex300. The video decoding apparatus may be implemented not in the set top box but in the television ex300.

[0097] Figure 9 illustrates the television (receiver) ex300 that uses the video coding method and the video decoding method described in each of embodiments. The television ex300 includes: a tuner ex301 that obtains or provides multiplexed data obtained by multiplexing audio data onto video data, through the antenna ex204 or the cable ex203, etc. that receives a broadcast; a modulation/demodulation unit ex302 that demodulates the received multiplexed data or modulates data into multiplexed data to be supplied outside; and a multiplexing/demultiplexing unit ex303 that demultiplexes the modulated multiplexed data into video data and audio data, or multiplexes video data and audio data coded by a signal processing unit ex306 into data.

[0098] The television ex300 further includes: a signal processing unit ex306 including an audio signal processing unit ex304 and a video signal processing unit ex305 that decode audio data and video data and code audio data and video data, respectively; and an output unit ex309 including a speaker ex307 that provides the decoded audio signal, and a display unit ex308 that displays the decoded video signal, such as a display. Furthermore, the television ex300 includes an interface unit ex317 including an operation input unit ex312 that receives an input of a user operation. Furthermore, the television ex300 includes a control unit ex310 that controls overall each constituent element of the television ex300, and a power supply circuit unit ex311 that supplies power to each of the elements. Other than the operation input unit ex312, the interface unit ex317 may include: a bridge ex313 that is connected to an external device, such as the reader/recorder ex218; a slot unit ex314 for enabling attachment of the recording medium ex216, such as an SD card; a driver ex315 to be connected to an external recording medium, such as a hard disk; and a modem ex316 to be connected to a telephone network. Here, the recording medium ex216 can electrically record information using a non-volatile/volatile semiconductor memory element for storage. The constituent elements of the television ex300 are connected to each other through a synchronous bus.

[0099] First, the configuration in which the television ex300 decodes multiplexed data obtained from outside through the antenna ex204 and others and reproduces the decoded data will be described. In the television ex300, upon a user operation through a remote controller ex220 and others, the multiplexing/demultiplexing unit ex303 demultiplexes the multiplexed data demodulated by the modulation/demodulation unit ex302, under control of the control unit ex310 including a CPU. Furthermore, the audio signal processing unit ex304 decodes the demultiplexed audio data, and the video signal processing unit ex305 decodes the demultiplexed video data, using the decoding method described in each of embodiments, in the television ex300. The output unit ex309 provides the decoded video signal and audio signal outside, respectively. When the output unit ex309 provides the video signal and the audio signal, the signals may be temporarily stored in buffers ex318 and ex319, and others so that the signals are reproduced in synchronization with each other. Furthermore, the television ex300 may read multiplexed data not through a broadcast and others but from the recording media ex215 and ex216, such as a magnetic disk, an optical disk, and a SD card. Next, a configuration in which the television ex300 codes an audio signal and a video signal, and transmits the data outside or writes the data on a recording medium will be described. In the television ex300, upon a user operation through the remote controller ex220 and others, the audio signal processing unit ex304 codes an audio signal, and the video signal processing unit ex305 codes a video signal, under control of the control unit ex310 using the coding method described in each of embodiments. The multiplexing/demultiplexing unit ex303 multiplexes the coded video signal and audio signal, and provides the resulting signal outside. When the multiplexing/demultiplexing unit ex303 multiplexes the video signal and the audio signal, the signals may be temporarily stored in the buffers ex320 and ex321, and others so that the signals are reproduced in synchronization with each other. Here, the buffers ex318, ex319, ex320, and ex321 may be plural as illustrated, or at least one buffer may be shared in the television ex300. Furthermore, data may be stored in a buffer so that the system overflow and underflow may be avoided between the modulation/demodulation unit ex302 and the multiplexing/demultiplexing unit ex303, for example.

[0100] Furthermore, the television ex300 may include a configuration for receiving an AV input from a microphone or a camera other than the configuration for obtaining audio and video data from a broadcast or a recording medium, and may code the obtained data. Although the television ex300 can code, multiplex, and provide outside data in the description, it may be capable of only receiving, decoding, and providing outside data but not the coding, multiplexing, and providing outside data.

[0101] Furthermore, when the reader/recorder ex218 reads or writes multiplexed data from or on a recording medium, one of the television ex300 and the reader/recorder ex218 may decode or code the multiplexed data, and the television ex300 and the reader/recorder ex218 may share the decoding or coding.

[0102] As an example, Figure 10 illustrates a configuration of an information reproducing/recording unit ex400 when data is read or written from or on an optical disk. The information reproducing/recording unit ex400 includes constituent elements ex401, ex402, ex403, ex404, ex405, ex406, and ex407 to be described hereinafter. The optical head ex401 irradiates a laser spot in a recording surface of the recording medium ex215 that is an optical disk to write information, and detects reflected light from the recording surface of the recording medium ex215 to read the information. The modulation recording unit ex402 electrically drives a semiconductor laser included in the optical head ex401, and modulates the laser light according to recorded data. The reproduction demodulating unit ex403 amplifies a reproduction signal obtained by electrically detecting the reflected light from the recording surface using a photo detector included in the optical head ex401, and demodulates the reproduction signal by separating a signal component recorded on the recording medium ex215 to reproduce the necessary information. The buffer ex404 temporarily holds the information to be recorded on the recording medium ex215 and the information reproduced from the recording medium ex215. The disk motor ex405 rotates the recording medium ex215. The servo control unit ex406 moves the optical head ex401 to a predetermined information track while controlling the rotation drive of the disk motor ex405 so as to follow the laser spot. The system control unit ex407 controls overall the information reproducing/recording unit ex400. The reading and writing processes can be implemented by the system control unit ex407 using various information stored in the buffer ex404 and generating and adding new information as necessary, and by the modulation recording unit ex402, the reproduction demodulating unit ex403, and the servo control unit ex406 that record and reproduce information through the optical head ex401 while being operated in a coordinated manner. The system control unit ex407 includes, for example, a microprocessor, and executes processing by causing a computer to execute a program for read and write.

[0103] Although the optical head ex401 irradiates a laser spot in the description, it may perform high-density recording using near field light.

[0104] Figure 11 illustrates the recording medium ex215 that is the optical disk. On the recording surface of the recording medium ex215, guide grooves are spirally formed, and an information track ex230 records, in advance, address information indicating an absolute position on the disk according to change in a shape of the guide grooves. The address information includes information for determining positions of recording blocks ex231 that are a unit for recording data. Reproducing the information track ex230 and reading the address information in an apparatus that records and reproduces data can lead to determination of the positions of the recording blocks. Furthermore, the recording medium ex215 includes a data recording area ex233, an inner circumference area ex232, and an outer circumference area ex234. The data recording area ex233 is an area for use in recording the user data. The inner circumference area ex232 and the outer circumference area ex234 that are inside and outside of the data recording area ex233, respectively are for specific use except for recording the user data. The information reproducing/recording unit 400 reads and writes coded audio, coded video data, or multiplexed data obtained by multiplexing the coded audio and video data, from and on the data recording area ex233 of the recording medium ex215.

[0105] Although an optical disk having a layer, such as a DVD and a BD is described as an example in the description, the optical disk is not limited to such, and may be an optical disk having a multilayer structure and capable of being recorded on a part other than the surface. Furthermore, the optical disk may have a structure for multidimensional recording/reproduction, such as recording of information using light of colors with different wavelengths in the same portion of the optical disk and for recording information having different layers from various angles.

[0106] Furthermore, a car ex210 having an antenna ex205 can receive data from the satellite ex202 and others, and reproduce video on a display device such as a car navigation system ex211 set in the car ex210, in the digital broadcasting system ex200. Here, a configuration of the car navigation system ex211 will be a configuration, for example, including a GPS receiving unit from the configuration illustrated in Figure 8. The same will be true for the configuration of the computer ex111, the cellular phone ex114, and others.

[0107] Figure 12 (a) illustrates the cellular phone ex114 that uses the video coding method and the video decoding method described in embodiments. The cellular phone ex114 includes: an antenna ex350 for transmitting and receiving radio waves through the base station ex110; a camera unit ex365 capable of capturing moving and still images; and a display unit ex358 such as a liquid crystal display for displaying the data such as decoded video captured by the camera unit ex365 or received by the antenna ex350. The cellular phone ex114 further includes: a main body unit including an operation key unit ex366; an audio output unit ex357 such as a speaker for output of audio; an audio input unit ex356 such as a microphone for input of audio; a memory unit ex367 for storing captured video or still pictures, recorded audio, coded or decoded data of the received video, the still pictures, e-mails, or others; and a slot unit ex364 that is an interface unit for a recording medium that stores data in the same manner as the memory unit ex367.

[0108] Next, an example of a configuration of the cellular phone ex114 will be described with reference to Figure 12 (b). In the cellular phone ex114, a main control unit ex360 designed to control overall each unit of the main body including the display unit ex358 as well as the operation key unit ex366 is connected mutually, via a synchronous bus ex370, to a power supply circuit unit ex361, an operation input control unit ex362, a video signal processing unit ex355, a camera interface unit ex363, a liquid crystal display (LCD) control unit ex359, a modulation/demodulation unit ex352, a multiplexing/demultiplexing unit ex353, an audio signal processing unit ex354, the slot unit ex364, and the memory unit ex367.

[0109] When a call-end key or a power key is turned ON by a user's operation, the power supply circuit unit ex361 supplies the respective units with power from a battery pack so as to activate the cell phone ex114.

[0110] In the cellular phone ex114, the audio signal processing unit ex354 converts the audio signals collected by the audio input unit ex356 in voice conversation mode into digital audio signals under the control of the main control unit ex360 including a CPU, ROM, and RAM. Then, the modulation/demodulation unit ex352 performs spread spectrum processing on the digital audio signals, and the transmitting and receiving unit ex351 performs digital-to-analog conversion and frequency conversion on the data, so as to transmit the resulting data via the antenna ex350.

[0111] Also, in the cellular phone ex114, the transmitting and receiving unit ex351 amplifies the data received by the antenna ex350 in voice conversation mode and performs frequency conversion and the analog-to-digital conversion on the data. Then, the modulation/demodulation unit ex352 performs inverse spread spectrum processing on the data, and the audio signal processing unit ex354 converts it into analog audio signals, so as to output them via the audio output unit ex356.

[0112] Furthermore, when an e-mail in data communication mode is transmitted, text data of the e-mail inputted by operating the operation key unit ex366 and others of the main body is sent out to the main control unit ex360 via the operation input control unit ex362. The main control unit ex360 causes the modulation/demodulation unit ex352 to perform spread spectrum processing on the text data, and the transmitting and receiving unit ex351 performs the digital-to-analog conversion and the frequency conversion on the resulting data to transmit the data to the base station ex110 via the antenna ex350. When an e-mail is received, processing that is approximately inverse to the processing for transmitting an e-mail is performed on the received data, and the resulting data is provided to the display unit ex358.

[0113] When video, still images, or video and audio in data communication mode is or are transmitted, the video signal processing unit ex355 compresses and codes video signals supplied from the camera unit ex365 using the video coding method shown in each of embodiments, and transmits the coded video data to the multiplexing/demultiplexing unit ex353. In contrast, during when the camera unit ex365 captures video, still images, and others, the audio signal processing unit ex354 codes audio signals collected by the audio input unit ex356, and transmits the coded audio data to the multiplexing/demultiplexing unit ex353.

[0114] The multiplexing/demultiplexing unit ex353 multiplexes the coded video data supplied from the video signal processing unit ex355 and the coded audio data supplied from the audio signal processing unit ex354, using a predetermined method.

[0115] Then, the modulation/demodulation unit ex352 performs spread spectrum processing on the multiplexed data, and the transmitting and receiving unit ex351 performs digital-to-analog conversion and frequency conversion on the data so as to transmit the resulting data via the antenna ex350.

[0116] When receiving data of a video file which is linked to a Web page and others in data communication mode or when receiving an e-mail with video and/or audio attached, in order to decode the multiplexed data received via the antenna ex350, the multiplexing/demultiplexing unit ex353 demultiplexes the multiplexed data into a video data bit stream and an audio data bit stream, and supplies the video signal processing unit ex355 with the coded video data and the audio signal processing unit ex354 with the coded audio data, through the synchronous bus ex370. The video signal processing unit ex355 decodes the video signal using a video decoding method corresponding to the coding method shown in each of embodiments, and then the display unit ex358 displays, for instance, the video and still images included in the video file linked to the Web page via the LCD control unit ex359. Furthermore, the audio signal processing unit ex354 decodes the audio signal, and the audio output unit ex357 provides the audio.

[0117] Furthermore, similarly to the television ex300, a terminal such as the cellular phone ex114 probably have 3 types of implementation configurations including not only (i) a transmitting and receiving terminal including both a coding apparatus and a decoding apparatus, but also (ii) a transmitting terminal including only a coding apparatus and (iii) a receiving terminal including only a decoding apparatus. Although the digital broadcasting system ex200 receives and transmits the multiplexed data obtained by multiplexing audio data onto video data in the description, the multiplexed data may be data obtained by multiplexing not audio data but character data related to video onto video data, and may be not multiplexed data but video data itself.

[0118] As such, the video coding method and the video decoding method in each of embodiments can be used in any of the devices and systems described. Thus, the advantages described in each of embodiments can be obtained.

[0119] Furthermore, the present invention is not limited to embodiments, and various modifications and revisions are possible without departing from the scope of the present invention.

[0120] Video data can be generated by switching, as necessary, between (i) the video coding method or the video coding apparatus shown in each of embodiments and (ii) a video coding method or a video coding apparatus in conformity with a different standard, such as MPEG-2, MPEG4-AVC, and VC-1.

[0121] Here, when a plurality of video data that conforms to the different standards is generated and is then decoded, the decoding methods need to be selected to conform to the different standards. However, since to which standard each of the plurality of the video data to be decoded conform cannot be detected, there is a problem that an appropriate decoding method cannot be selected.

[0122] In order to solve the problem, multiplexed data obtained by multiplexing audio data and others onto video data has a structure including identification information indicating to which standard the video data conforms. The specific structure of the multiplexed data including the video data generated in the video coding method and by the video coding apparatus shown in each of embodiments will be hereinafter described. The multiplexed data is a digital stream in the MPEG2-Transport Stream format.

[0123] Figure 13 illustrates a structure of the multiplexed data. As illustrated in Figure 13, the multiplexed data can be obtained by multiplexing at least one of a video stream, an audio stream, a presentation graphics stream (PG), and an interactive graphics stream. The video stream represents primary video and secondary video of a movie, the audio stream (IG) represents a primary audio part and a secondary audio part to be mixed with the primary audio part, and the presentation graphics stream represents subtitles of the movie. Here, the primary video is normal video to be displayed on a screen, and the secondary video is video to be displayed on a smaller window in the primary video. Furthermore, the interactive graphics stream represents an interactive screen to be generated by arranging the GUI components on a screen. The video stream is coded in the video coding method or by the video coding apparatus shown in each of embodiments, or in a video coding method or by a video coding apparatus in conformity with a conventional standard, such as MPEG-2, MPEG4-AVC, and VC-1. The audio stream is coded in accordance with a standard, such as Dolby-AC-3, Dolby Digital Plus, MLP, DTS, DTS-HD, and linear PCM.

[0124] Each stream included in the multiplexed data is identified by PID. For example, 0x1011 is allocated to the video stream to be used for video of a movie, 0x1100 to 0x111F are allocated to the audio streams, 0x1200 to 0x121 F are allocated to the presentation graphics streams, 0x1400 to 0x141 F are allocated to the interactive graphics streams, 0x1B00 to 0x1B1Fare allocated to the video streams to be used for secondary video of the movie, and 0x1A00 to 0x1A1F are allocated to the audio streams to be used for the secondary video to be mixed with the primary audio.

[0125] Figure 14 schematically illustrates how data is multiplexed. First, a video stream ex235 composed of video frames and an audio stream ex238 composed of audio frames are transformed into a stream of PES packets ex236 and a stream of PES packets ex239, and further into TS packets ex237 and TS packets ex240, respectively. Similarly, data of a presentation graphics stream ex241 and data of an interactive graphics stream ex244 are transformed into a stream of PES packets ex242 and a stream of PES packets ex245, and further into TS packets ex243 and TS packets ex246, respectively. These TS packets are multiplexed into a stream to obtain multiplexed data ex247.

[0126] Figure 15 illustrates how a video stream is stored in a stream of PES packets in more detail. The first bar in Figure 15 shows a video frame stream in a video stream. The second bar shows the stream of PES packets. As indicated by arrows denoted as yy1, yy2, yy3, and yy4 in Figure 15, the video stream is divided into pictures as I pictures, B pictures, and P pictures each of which is a video presentation unit, and the pictures are stored in a payload of each of the PES packets. Each of the PES packets has a PES header, and the PES header stores a Presentation Time-Stamp (PTS) indicating a display time of the picture, and a Decoding Time-Stamp (DTS) indicating a decoding time of the picture.

[0127] Figure 16 illustrates a format of TS packets to be finally written on the multiplexed data. Each of the TS packets is a 188-byte fixed length packet including a 4-byte TS header having information, such as a PID for identifying a stream and a 184-byte TS payload for storing data. The PES packets are divided, and stored in the TS payloads, respectively. When a BD ROM is used, each of the TS packets is given a 4-byte TP_Extra_Header, thus resulting in 192-byte source packets. The source packets are written on the multiplexed data. The TP_Extra_Header stores information such as an Arrival Time Stamp (ATS). The ATS shows a transfer start time at which each of the TS packets is to be transferred to a PID filter. The source packets are arranged in the multiplexed data as shown at the bottom of Figure 16. The numbers incrementing from the head of the multiplexed data are called source packet numbers (SPNs).

[0128] Each of the TS packets included in the multiplexed data includes not only streams of audio, video, subtitles and others, but also a Program Association Table (PAT), a Program Map Table (PMT), and a Program Clock Reference (PCR). The PAT shows what a PID in a PMT used in the multiplexed data indicates, and a PID of the PAT itself is registered as zero. The PMT stores PIDs of the streams of video, audio, subtitles and others included in the multiplexed data, and attribute information of the streams corresponding to the PIDs. The PMT also has various descriptors relating to the multiplexed data. The descriptors have information such as copy control information showing whether copying of the multiplexed data is permitted or not. The PCR stores STC time information corresponding to an ATS showing when the PCR packet is transferred to a decoder, in order to achieve synchronization between an Arrival Time Clock (ATC) that is a time axis of ATSs, and an System Time Clock (STC) that is a time axis of PTSs and DTSs.

[0129] Figure 17 illustrates the data structure of the PMT in detail. A PMT header is disposed at the top of the PMT. The PMT header describes the length of data included in the PMT and others. A plurality of descriptors relating to the multiplexed data is disposed after the PMT header. Information such as the copy control information is described in the descriptors. After the descriptors, a plurality of pieces of stream information relating to the streams included in the multiplexed data is disposed. Each piece of stream information includes stream descriptors each describing information, such as a stream type for identifying a compression codec of a stream, a stream PID, and stream attribute information (such as a frame rate or an aspect ratio). The stream descriptors are equal in number to the number of streams in the multiplexed data.

[0130] When the multiplexed data is recorded on a recording medium and others, it is recorded together with multiplexed data information files.

[0131] Each of the multiplexed data information files is management information of the multiplexed data as shown in Figure 18. The multiplexed data information files are in one to one correspondence with the multiplexed data, and each of the files includes multiplexed data information, stream attribute information, and an entry map.

[0132] As illustrated in Figure 18, the multiplexed data includes a system rate, a reproduction start time, and a reproduction end time. The system rate indicates the maximum transfer rate at which a system target decoder to be described later transfers the multiplexed data to a PID filter. The intervals of the ATSs included in the multiplexed data are set to not higher than a system rate. The reproduction start time indicates a PTS in a video frame at the head of the multiplexed data. An interval of one frame is added to a PTS in a video frame at the end of the multiplexed data, and the PTS is set to the reproduction end time.

[0133] As shown in Figure 19, a piece of attribute information is registered in the stream attribute information, for each PID of each stream included in the multiplexed data. Each piece of attribute information has different information depending on whether the corresponding stream is a video stream, an audio stream, a presentation graphics stream, or an interactive graphics stream. Each piece of video stream attribute information carries information including what kind of compression codec is used for compressing the video stream, and the resolution, aspect ratio and frame rate of the pieces of picture data that is included in the video stream. Each piece of audio stream attribute information carries information including what kind of compression codec is used for compressing the audio stream, how many channels are included in the audio stream, which language the audio stream supports, and how high the sampling frequency is. The video stream attribute information and the audio stream attribute information are used for initialization of a decoder before the player plays back the information.

[0134] The multiplexed data to be used is of a stream type included in the PMT. Furthermore, when the multiplexed data is recorded on a recording medium, the video stream attribute information included in the multiplexed data information is used. More specifically, the video coding method or the video coding apparatus described in each of embodiments includes a step or a unit for allocating unique information indicating video data generated by the video coding method or the video coding apparatus in each of embodiments, to the stream type included in the PMT or the video stream attribute information. With the configuration, the video data generated by the video coding method or the video coding apparatus described in each of embodiments can be distinguished from video data that conforms to another standard.

[0135] Furthermore, Figure 20 illustrates steps of the video decoding method. In Step exS100, the stream type included in the PMT or the video stream attribute information is obtained from the multiplexed data. Next, in Step exS101, it is determined whether or not the stream type or the video stream attribute information indicates that the multiplexed data is generated by the video coding method or the video coding apparatus in each of embodiments. When it is determined that the stream type or the video stream attribute information indicates that the multiplexed data is generated by the video coding method or the video coding apparatus in each of embodiments, in Step exS102, decoding is performed by the video decoding method in each of embodiments. Furthermore, when the stream type or the video stream attribute information indicates conformance to the conventional standards, such as MPEG-2, MPEG4-AVC, and VC-1, in Step exS103, decoding is performed by a video decoding method in conformity with the conventional standards.

[0136] As such, allocating a new unique value to the stream type or the video stream attribute information enables determination whether or not the video decoding method or the video decoding apparatus that is described in each of embodiments can perform decoding. Even when multiplexed data that conforms to a different standard, an appropriate decoding method or apparatus can be selected. Thus, it becomes possible to decode information without any error. Furthermore, the video coding method or apparatus, or the video decoding method or apparatus can be used in the devices and systems described above.

[0137] Each of the video coding method, the video coding apparatus, the video decoding method, and the video decoding apparatus in each of embodiments is typically achieved in the form of an integrated circuit or a Large Scale Integrated (LSI) circuit. As an example of the LSI, Figure 21 illustrates a configuration of the LSI ex500 that is made into one chip. The LSI ex500 includes elements ex501, ex502, ex503, ex504, ex505, ex506, ex507, ex508, and ex509 to be described below, and the elements are connected to each other through a bus ex510. The power supply circuit unit ex505 is activated by supplying each of the elements with power when the power supply circuit unit ex505 is turned on.

[0138] For example, when coding is performed, the LSI ex500 receives an AV signal from a microphone ex117, a camera ex113, and others through an AV IO ex509 under control of a control unit ex501 including a CPU ex502, a memory controller ex503, a stream controller ex504, and a driving frequency control unit ex512. The received AV signal is temporarily stored in an external memory ex511, such as an SDRAM. Under control of the control unit ex501, the stored data is segmented into data portions according to the processing amount and speed to be transmitted to a signal processing unit ex507. Then, the signal processing unit ex507 codes an audio signal and/or a video signal. Here, the coding of the video signal is the coding described in each of embodiments. Furthermore, the signal processing unit ex507 sometimes multiplexes the coded audio data and the coded video data, and a stream IO ex506 provides the multiplexed data outside. The provided multiplexed data is transmitted to the base station ex107, or written on the recording media ex215. When data sets are multiplexed, the data should be temporarily stored in the buffer ex508 so that the data sets are synchronized with each other.

[0139] Although the memory ex511 is an element outside the LSI ex500, it may be included in the LSI ex500. The buffer ex508 is not limited to one buffer, but may be composed of buffers. Furthermore, the LSI ex500 may be made into one chip or a plurality of chips.

[0140] Furthermore, although the control unit ex510 includes the CPU ex502, the memory controller ex503, the stream controller ex504, the driving frequency control unit ex512, the configuration of the control unit ex510 is not limited to such. For example, the signal processing unit ex507 may further include a CPU. Inclusion of another CPU in the signal processing unit ex507 can improve the processing speed. Furthermore, as another example, the CPU ex502 may serve as or be a part of the signal processing unit ex507, and, for example, may include an audio signal processing unit. In such a case, the control unit ex501 includes the signal processing unit ex507 or the CPU ex502 including a part of the signal processing unit ex507.

[0141] The name used here is LSI, but it may also be called IC, system LSI, super LSI, or ultra LSI depending on the degree of integration.

[0142] Moreover, ways to achieve integration are not limited to the LSI, and a special circuit or a general purpose processor and so forth can also achieve the integration. Field Programmable Gate Array (FPGA) that can be programmed after manufacturing LSIs or a reconfigurable processor that allows re-configuration of the connection or configuration of an LSI can be used for the same purpose.

[0143] In the future, with advancement in semiconductor technology, a brand-new technology may replace LSI. The functional blocks can be integrated using such a technology. The possibility is that the present invention is applied to biotechnology.

[0144] When video data generated in the video coding method or by the video coding apparatus described in each of embodiments is decoded, compared to when video data that conforms to a conventional standard, such as MPEG-2, MPEG4-AVC, and VC-1 is decoded, the processing amount probably increases. Thus, the LSI ex500 needs to be set to a driving frequency higher than that of the CPU ex502 to be used when video data in conformity with the conventional standard is decoded. However, when the driving frequency is set higher, there is a problem that the power consumption increases.

[0145] In order to solve the problem, the video decoding apparatus, such as the television ex300 and the LSI ex500 is configured to determine to which standard the video data conforms, and switch between the driving frequencies according to the determined standard. Figure 22 illustrates a configuration ex800. A driving frequency switching unit ex803 sets a driving frequency to a higher driving frequency when video data is generated by the video coding method or the video coding apparatus described in each of embodiments. Then, the driving frequency switching unit ex803 instructs a decoding processing unit ex801 that executes the video decoding method described in each of embodiments to decode the video data. When the video data conforms to the conventional standard, the driving frequency switching unit ex803 sets a driving frequency to a lower driving frequency than that of the video data generated by the video coding method or the video coding apparatus described in each of embodiments. Then, the driving frequency switching unit ex803 instructs the decoding processing unit ex802 that conforms to the conventional standard to decode the video data.

[0146] More specifically, the driving frequency switching unit ex803 includes the CPU ex502 and the driving frequency control unit ex512 in Figure 21. Here, each of the decoding processing unit ex801 that executes the video decoding method described in each of embodiments and the decoding processing unit ex802 that conforms to the conventional standard corresponds to the signal processing unit ex507 in Figure 21. The CPU ex502 determines to which standard the video data conforms. Then, the driving frequency control unit ex512 determines a driving frequency based on a signal from the CPU ex502. Furthermore, the signal processing unit ex507 decodes the video data based on the signal from the CPU ex502. For example, the identification information described is probably used for identifying the video data. The identification information is not limited to the one described above but may be any information as long as the information indicates to which standard the video data conforms. For example, when which standard video data conforms to can be determined based on an external signal for determining that the video data is used for a television or a disk, etc., the determination may be made based on such an external signal. Furthermore, the CPU ex502 selects a driving frequency based on, for example, a look-up table in which the standards of the video data are associated with the driving frequencies as shown in Figure 24. The driving frequency can be selected by storing the look-up table in the buffer ex508 and in an internal memory of an LSI, and with reference to the look-up table by the CPU ex502.

[0147] Figure 23 illustrates steps for executing a method. First, in Step exS200, the signal processing unit ex507 obtains identification information from the multiplexed data. Next, in Step exS201, the CPU ex502 determines whether or not the video data is generated by the coding method and the coding apparatus described in each of embodiments, based on the identification information. When the video data is generated by the video coding method and the video coding apparatus described in each of embodiments, in Step exS202, the CPU ex502 transmits a signal for setting the driving frequency to a higher driving frequency to the driving frequency control unit ex512. Then, the driving frequency control unit ex512 sets the driving frequency to the higher driving frequency. On the other hand, when the identification information indicates that the video data conforms to the conventional standard, such as MPEG-2, MPEG4-AVC, and VC-1, in Step exS203, the CPU ex502 transmits a signal for setting the driving frequency to a lower driving frequency to the driving frequency control unit ex512. Then, the driving frequency control unit ex512 sets the driving frequency to the lower driving frequency than that in the case where the video data is generated by the video coding method and the video coding apparatus described in each of embodiment.

[0148] Furthermore, along with the switching of the driving frequencies, the power conservation effect can be improved by changing the voltage to be applied to the LSI ex500 or an apparatus including the LSI ex500. For example, when the driving frequency is set lower, the voltage to be applied to the LSI ex500 or the apparatus including the LSI ex500 is probably set to a voltage lower than that in the case where the driving frequency is set higher.

[0149] Furthermore, when the processing amount for decoding is larger, the driving frequency may be set higher, and when the processing amount for decoding is smaller, the driving frequency may be set lower as the method for setting the driving frequency. Thus, the setting method is not limited to the ones described above. For example, when the processing amount for decoding video data in conformity with MPEG 4 -AVC is larger than the processing amount for decoding video data generated by the video coding method and the video coding apparatus described in each of embodiments, the driving frequency is probably set in reverse order to the setting described above.

[0150] Furthermore, the method for setting the driving frequency is not limited to the method for setting the driving frequency lower. For example, when the identification information indicates that the video data is generated by the video coding method and the video coding apparatus described in each of embodiments, the voltage to be applied to the LSI ex500 or the apparatus including the LSI ex500 is probably set higher. When the identification information indicates that the video data conforms to the conventional standard, such as MPEG-2, MPEG4-AVC, and VC-1, the voltage to be applied to the LSI ex500 or the apparatus including the LSI ex500 is probably set lower. As another example, when the identification information indicates that the video data is generated by the video coding method and the video coding apparatus described in each of embodiments, the driving of the CPU ex502 does not probably have to be suspended. When the identification information indicates that the video data conforms to the conventional standard, such as MPEG-2, MPEG4-AVC, and VC-1, the driving of the CPU ex502 is probably suspended at a given time because the CPU ex502 has extra processing capacity. Even when the identification information indicates that the video data is generated by the video coding method and the video coding apparatus described in each of embodiments, in the case where the CPU ex502 has extra processing capacity, the driving of the CPU ex502 is probably suspended at a given time. In such a case, the suspending time is probably set shorter than that in the case where when the identification information indicates that the video data conforms to the conventional standard, such as MPEG-2, MPEG4-AVC, and VC-1.

[0151] Accordingly, the power conservation effect can be improved by switching between the driving frequencies in accordance with the standard to which the video data conforms. Furthermore, when the LSI ex500 or the apparatus including the LSI ex500 is driven using a battery, the battery life can be extended with the power conservation effect.

[0152] There are cases where a plurality of video data that conforms to different standards, is provided to the devices and systems, such as a television and a mobile phone. In order to enable decoding the plurality of video data that conforms to the different standards, the signal processing unit ex507 of the LSI ex500 needs to conform to the different standards. However, the problems of increase in the scale of the circuit of the LSI ex500 and increase in the cost arise with the individual use of the signal processing units ex507 that conform to the respective standards.

[0153] In order to solve the problem, what is conceived is a configuration in which the decoding processing unit for implementing the video decoding method described in each of embodiments and the decoding processing unit that conforms to the conventional standard, such as MPEG-2, MPEG4-AVC, and VC-1 are partly shared. Ex900 in Figure 25(a) shows an example of the configuration. For example, the video decoding method described in each of embodiments and the video decoding method that conforms to MPEG4-AVC have, partly in common, the details of processing, such as entropy coding, inverse quantization, deblocking filtering, and motion compensated prediction. The details of processing to be shared probably includes use of a decoding processing unit ex902 that conforms to MPEG4-AVC. In contrast, a dedicated decoding processing unit ex901 is probably used for other processing unique to the present invention. Since the present invention is characterized by a spatial prediction, for example, the dedicated decoding processing unit ex901 is used for spatial prediction in accordance with the present invention. Otherwise, the decoding processing unit is probably shared for one of the entropy coding, inverse transformation, inverse quantization, and motion compensated prediction, or all of the processing. The decoding processing unit for implementing the video decoding method described in each of embodiments may be shared for the processing to be shared, and a dedicated decoding processing unit may be used for processing unique to that of MPEG4-AVC.

[0154] Furthermore, ex1000 in Figure 25(b) shows another example in that processing is partly shared. This example uses a configuration including a dedicated decoding processing unit ex1001 that supports the processing unique to the present invention, a dedicated decoding processing unit ex1002 that supports the processing unique to another conventional standard, and a decoding processing unit ex1003 that supports processing to be shared between the video decoding method in the present invention and the conventional video decoding method. Here, the dedicated decoding processing units ex1001 and ex1002 are not necessarily specialized for the processing of the present invention and the processing of the conventional standard, respectively, and may be the ones capable of implementing general processing. Furthermore, the configuration can be implemented by the LSI ex500.

[0155] As such, reducing the scale of the circuit of an LSI and reducing the cost are possible by sharing the decoding processing unit for the processing to be shared between the video decoding method in the present invention and the video decoding method in conformity with the conventional standard. Summarizing, the present invention relates to an efficient implementation of a directional spatial prediction. The directional spatial prediction includes detecting an edge by means of determining a vertical and a horizontal gradient within an adjacent block, determining for each pixel to be predicted an intersection of the detected edge with a boundary row or a column of pixels of the adjacent block, and extrapolating or interpolating each pixel in the block according to the determined intersection. The intersection may be a sub-pel position. In particular, the calculation of the intersection includes dividing by a vertical or a horizontal gradient to obtain an integer slope common for the entire block to be predicted. This reduces the number of divisions to one per block. In order to increase the precision of the division, a scaling by a scaling factor depending on a value of a horizontal or vertical gradient, respectively, may be applied.

Claims

1. A method for spatially predicting the values at each pixel position of a block of pixels in an image, the method comprising the steps of:

detecting an edge (E) entering the block by obtaining its horizontal gradient (Gy) and its vertical gradient (Gx);

obtaining an integer value of a slope of the detected edge (E) based on the obtained horizontal gradient (Gy) and/or vertical gradient (Gx);

determining for each pixel (440) a sub-pel position (450) within a closest row or column of pixels of a neighbouring block, the sub-pel position (450) being calculated as an intersection of said row or column of pixels with a line (430) having the obtained integer value slope and passing through said pixel (440); and

predicting each pixel (440) in the block based on an interpolated value of the sub-pel position (450) calculated for said pixel (440).

2. The method according to claim 1 wherein
the step of obtaining the integer slope includes scaling with a c-th power of 2, c being a positive integer; and
the step of determining for each pixel (440) a sub-pel position (450) comprises multiplying the scaled slope with a column or row coordinate of said pixel within the block to be predicted .

3. The method according to claim 2 wherein the value c is a function of the horizontal (Gy) or the vertical (Gx) gradient.

4. The method according to any of claims 1 to 3 wherein
the step of obtaining the integer slope includes dividing by the vertical (Gx) or the horizontal (Gy) gradient implemented by retrieving the result of the division from a division table stored in a memory.

5. The method according to claim 4 wherein
the division table has a limited number of entries for values of the vertical (Gx) gradient or horizontal (Gy) gradient up to b-th power of 2, b being an integer; and when the value of the vertical (Gx) or the horizontal (Gy) gradient exceeds the b-th power of 2, the vertical (Gx) and the horizontal (Gy) gradient are scaled by shifting their value one bit right.

6. The method according to any of claims 1 to 5 wherein
the step of obtaining the integer slope includes dividing the vertical gradient (Gx) by the horizontal gradient (Gy) or dividing the horizontal gradient (Gy) by the vertical gradient (Gx); and
the step of predicting includes for each pixel interpolating said sub-pel position as a weighed average of full-pel positions closest to the determined sub-pel position within the row or the column of pixels, the weights being set according to the distance of the closest pixels and the determined sub-pel position.

7. A method for decoding of an image subdivided into a plurality of pixels blocks, the method comprising the step of
obtaining a prediction signal block (122, 222) as a result of predicting a current block of pixels (440) in accordance with the method of any of claims 1 to 6; and computing (225) a reconstructed image block by adding the obtained prediction signal block to a decoded prediction error block.

8. A computer program product comprising a computer-readable medium having a computer-readable program code embodied thereon, the program code being adapted to carry out the method according to any of claims 1 to 7.

9. An apparatus for spatially predicting the values at each pixel position of a block of pixels in an image, the apparatus comprising:

an edge detector for detecting an edge (E) entering the block by obtaining its horizontal gradient (Gy) and its vertical gradient (Gx);

an intersection determining unit for obtaining an integer value of a slope of the detected edge (E) based on the obtained horizontal gradient (Gy) and/or vertical gradient (Gx), and for determining for each pixel (440) a sub-pel position (450) within a closest row or column of pixels of a neighbouring block, the sub-pel position (450) being calculated as an intersection of said row or column of pixels with a line (430) having the obtained integer value slope and passing through said pixel (440); and

a prediction unit for predicting each pixel (440) in the block based on the sub-pel position (450) calculated for said pixel (440).

10. The apparatus according to claim 9 wherein
the intersection determining unit is configured to perform for obtaining the integer slope a scaling with a c-th power of 2, c being an integer; and
to multiply, for determining the sub-pel position (450) for each pixel, the scaled slope with a column or row coordinate of said pixel within the block to be predicted.

11. The apparatus according to claim 10 wherein the value c is a function of the horizontal (Gy) or the vertical (Gx) gradient.

12. The apparatus according to any of claims 9 to 11 wherein
the intersection determining unit is configured to obtain the integer slope including dividing by a vertical (Gx) or a horizontal (Gy) gradient, the division being performed by retrieving the result of the division from a division table stored in a memory.

13. The apparatus according to claim 12 wherein
the division table has a limited number of entries for values of the vertical (Gx) gradient or horizontal (Gy) gradient up to b-th power of 2, b being an integer; and when the value of the vertical (Gx) or the horizontal (Gy) gradient exceeds the b-the power of 2, the vertical (Gx) and the horizontal (Gy) gradient are scaled by shifting their value one bit right.

14. The apparatus according to any of claims 9 to 13 wherein
the intersection determining unit is configured to obtain the integer slope including dividing the vertical gradient (Gx) by the horizontal gradient (Gy) or dividing the horizontal gradient (Gy) by the vertical gradient (Gx); and
the prediction unit is configured to calculate each pixel as a weighed average of full-pel positions closest to the determined sub-pel position within the row or the column of pixels, the weights being set according to the distance of the closest pixels and the determined sub-pel position.

15. A decoder for decoding an image subdivided into a plurality of pixels blocks, the decoder comprising:

an intra predictor for obtaining a prediction signal block (122, 222) as a result of predicting a current block of pixels (440) by the apparatus for spatially predicting in accordance with any of claims 9 to 14; and

reconstructor for computing (225) a reconstructed image block by adding the obtained prediction signal block to a decoded prediction error block.

Drawing